EP0273185B1 - Roll with an adjustable linear contact pressure - Google Patents

Description

The invention relates to a roller of the type corresponding to the preamble of claim 1.

Such a roller is known from DE-C 30 03 395. In the known embodiment, the space between the crosshead and the inner circumference of the hollow roll is by longitudinal seals arranged along the crosshead on both sides of the active plane of the roll between the crosshead and the inner circumference of the hollow roll, past which the hollow roll slides past with its inner circumference into one on the side of the roll gap and divided a longitudinal chamber on the opposite side. At least the longitudinal chamber located on the side of the roll gap can be filled with pressure fluid, the pressure acting against the inner circumference of the hollow roll producing the line pressure in the roll gap. The zones of reduced pressure are located in this longitudinal chamber and form irregularities in the otherwise uniform pressure cushion, by means of which the pressure applied can be modified in a certain way. The decisive factor here is the presence of a subdivision formed by the longitudinal seals, through which the longitudinal chambers are divided, the pressure difference between which gives the line pressure.

The invention has for its object to provide a roller corresponding to the preamble, with which other options for influencing line printing are given, which can otherwise only be achieved with considerably greater effort, if at all.

This object is achieved by the feature reproduced in the characterizing part of claim 1.

Thus, while in DE-C 30 03 395 in the space between the crosshead and the inner circumference of the hollow roll, a longitudinal chamber located on the side of the roll gap is divided by the longitudinal seals, the pressure fluid of which pressure is uniform over the length of the roll against the inner circumference of the hollow roll and thus generates a corresponding line pressure, in the invention, the pressure fluid in the space between the crosshead and the inner circumference of the roller no longer acts on one side against the roll gap in order to generate the line pressure or a portion thereof. Rather, the pressure fluid exerts its pressure uniformly in all directions over the entire circumference, so that its force effect would be neutral without additional measures and would not affect the hollow roller at all with the exception of the generation of a uniform internal pressure.

In the preferred embodiment of the invention, the uniform pressure is naturally generated in such a way that there are no longitudinal seals at all. This eliminates the structural effort involved and there is also no loss of performance due to the friction on the longitudinal seals. But even if a roller has longitudinal seals for certain operating modes, the same pressure everywhere can be artificially created by a throttle-free connecting channel between the longitudinal chambers divided by the longitudinal seals.

The effect of the invention is now based on the fact that the zones of reduced pressure divided by the sealing members create an asymmetry in the all-round application of pressure by the hydraulic fluid, which leads to the result that the resulting forces remain on the hollow roller, which they seek to displace or when they pass through a counter roll is supported, lead to a line pressure in the nip formed.

If, for example, the zones of reduced pressure are arranged on the side opposite the roll gap, the fact arises from the fact that the pressure fluid exerts its pressure in the zones on the side of the roll gap which are mirror images of the meridian plane, but not on the opposite side, one against the other force directed to the roll gap, which leads to a line pressure distribution which is particularly characterized by the fact that the elements leading to the line pressure lie on the side remote from the roll gap. There, "holes" or "vacancies" are created in the otherwise uniform pressure distribution, which are matched by corresponding zones of uniform full pressure on the side of the roll gap, which act like pressure stamps directed against the roll gap.

If the zones of reduced pressure are located on the side of the roll gap, then the full pressure in the corresponding zones on the opposite side results in a resultant force which the hollow roll tends to pull away from the roll gap. This can be used both to influence the line pressure profile if the line pressure is generated as a whole by external means, for example back-up rolls which act on the hollow roll. The force of the backup rolls then overlaps the resulting local force components given by the "holes" or "vacancies". The arrangement can also be used to generate a so-called "inner stroke" through which the roll gap is lifted. The inner stroke is possible for rolls in which the hollow roll is not supported at the ends on the crosshead, but in the working plane, i.e. in the plane connecting the axes of the roller and the counter roller, can be displaced radially relative to the crosshead as a whole.

The basic principle of the invention is therefore based on producing "holes" of low pressure in the space filled with hydraulic fluid all around, in order to achieve certain force effects.

The possible variations in the line pressure curve generated can be considerably increased if the configuration according to claim 2, which represents an important extension of the invention, is provided.

The basic idea here is that one and the same zone either as a "hole" or "empty space" with one in relation to the environment lower pressure and, on the other hand, can also be operated as a positive pressure member with a pressure which is higher than the pressure of the environment, ie as a "vacuum element" or as a "pressure element".

Of course, this significantly increases the range of options for influencing line printing.

An important aspect here is that with a zone located on only one side of the crosshead and divided off by appropriate sealing members, both the inner circumference of the hollow roller can be “sucked in” against the crosshead and “pushed away”. In order to achieve such effects, elements located on different sides of the crosshead have so far been required, which required corresponding bores in the crosshead and accordingly weakened it.

The basic device-like design of the elements for forming the zones is given in claim 3.

The "stamp" combine the functions of the pressure pieces according to DE-A 22 30 139 and the annular sealing members according to DE-C 30 03 395. The problem is that if the stamps are to work as overpressure elements and accordingly in the cylinder chamber there is high pressure, the plunger must be sealed against this pressure except for the throttle bores so that the required pressure can take place on the inner circumference of the hollow roller. However, if the plunger is to function as a vacuum element, hydraulic fluid flowing into the hydrostatic pressure chamber must be unhindered, i.e. can flow off without appreciable pressure build-up. The flow resistance must therefore be different in the two directions. For this purpose, the additional check valves are arranged in the stamps, the basic structure of which corresponds to the pressure pieces of DE-A 22 30 139.

DE-B 23 32 861 alone is known per se from supporting elements working as overpressure elements in a one-sided longitudinal chamber of a conventional type, which are hydraulically connected in series.

In the simplest embodiment, the throttle bores are connected to the cylinder space.

The pressure fluid supplied to the cylinder space pushes the plunger against the inner circumference of the hollow roller during operation as an overpressure element, the pressure fluid required to build up the hydrostatic pressure flowing into the hydrostatic pressure chambers from the cylinder space through the throttle bores.

In this case, only a pressure needs to be supplied to the cylinder space.

In an alternative embodiment according to claim 5, the feed lines to the cylinder space and to the hydrostatic chamber are separated. The pressure in the hydrostatic chamber does not therefore set itself, but must be controlled externally depending on the pressure in the cylinder space.

An important design for the satisfactory functionality in practice are the upstream discharge chambers according to claim 6. The discharge chambers in both operating states of the plunger as an overpressure element and underpressure element take up the pressure fluid carried by adhering to the inner circumference of the hollow roller by adhering to the inner circumference of the hollow roller trap it before it can get into the lower pressure area.

For example, if the plunger works as an overpressure element and there is a higher pressure in the cylinder space than in the space between the crosshead and the hollow roller, a certain amount of pressure fluid constantly passes from the hydrostatic pressure chamber into the space without special precautions. This can lead to problems, for example, if the pressure fluid in the intermediate space and the pressure fluid in the cylinder space have different temperatures. The extracted hydraulic fluid then creates an annular, colder zone on the inner circumference of the hollow roller, which causes temperature irregularities along the hollow roller; that can make themselves noticeable.

In the other case, if the pressure in the space between the crosshead and the hollow roller is higher than in the cylinder space, hydraulic fluid is introduced from the cylinder space into the area of the hydrostatic pressure chamber without special precautions and there may be a reason for a build-up of pressure that distorts the desired function. The pressure fluid that is carried in over the edge of the stamp is intercepted beforehand by the discharge chamber.

A special embodiment is the subject of claim 7.

The overhang at the edge of the stamp is necessary since it is necessary for the stamp to function properly as a pressure element that the supporting cross section of the hydrostatic pressure chamber is larger than the cross section of the cylinder. This can only be accomplished if the support surface of the plunger bearing against the inner circumference of the hollow roller is larger than its piston-like part. This inevitably leads to an overhang. If the stamp is operated as a vacuum element, then the higher pressure in the space between the crosshead and the hollow roller engages under the overhang and presses the stamp with appropriate force against the inner circumference of the hollow roller. At high pressures in the intermediate space, this force can For this reason, a pressure relief is created, so that when operating as a vacuum element, the high pressure of the intermediate space is supplied to the inner chamber of the plunger via the check valve and from there via the throttle bores to the hydrostatic pressure chamber which counteracts the pressure acting against the overhang and relieves the pressure on the stamp. It is understood that the cross sections are suitably adapted here.

According to claim 8, the cylinder chamber can be connected to the discharge chamber via a throttle bore.

As a result, when the plunger is operated as an overpressure element, the cross section of the discharge chamber can also be used to exert hydrostatic pressure.

An expedient embodiment is the subject of claim 9.

The hydrostatic pressure chamber lies like an island inside the discharge chamber. In this way, its cross section can be adapted to the cross section of the overhang, so that the force aimed at pushing the stamp away from the inner circumference of the hollow roller does not become too great. Nevertheless, a large cross-section is available for operation as an overpressure element, namely the cross-section of the actual hydrostatic pressure chamber and the discharge chamber.

In the preferred embodiment according to claim 10, the punches are all arranged on one side of the crosshead, namely on the side of the roll gap.

The advantage here is that with such an arrangement, the hollow roller is attracted with positive force both from the roll gap against the crosshead and against the roll gap from. Querahupt can be pushed away. One application is a roller with an internal stroke, which can be lifted with force, for example, even if the roll gap is below and ventilation must take place against the weight of the hollow roller. At the same time, line pressure can also be applied.

• Fig. 1 zeigt schematisch die Ansicht eines Walzenpaars, von dem die obere Walze als erfindungsgemäße Walze mit Zonen gegenüber dem Zwischenraum zwischen Querhaupt und Hohlwalze erniedrigten Drucks ausgebildet ist, teilweise im Schnitt;
• Fig. 2 zeigt einen Querschnitt gemäß der Linie II-11 in Fig. 1 in leicht vergrößertem Maßstab;
• Fig. 3 zeigt eine Ansicht entsprechend Fig. 1 eines Walzenpaars, bei welchem die Oberwalze mit Stempeln ausgerüstet ist, die sowohl als Unterdruckelemente als auch als Überdruckelemente arbeiten können;
• Fig. 4 zeigt einen Schnitt nach der Linie IV-IV in Fig. 3;
• Fig. 5 zeigt einen vergrößerten Teilquerschnitt durch eine erfindungsgemäße Walze mit einer ersten Ausführungsform eines Stempels;
• Fig. 6 zeigt einen Querschnitt entsprechend Fig. 5 in verkleinertem Maßstab, worin der hydraulische Schaltplan der Walze nach Fig. 5 angegeben ist;
• Fig. 7 zeigt eine Ansicht auf den Stempel nach Fig. 5 von oben;
• Fig. 8 zeigt schematisch einen Kalanderstapel, in welchem die erfindungsgemäße Walze schraffiert angedeutet ist;
• Fig. 9 zeigt einen Teillängsschnitt durch das Ende einer erfindungsgemäßen Walze mit innerem Hub;
• Fig. 10, 11 und 12 zeigen den Fig. 5, 6 und 7 entsprechende Ansichten einer weiteren Ausführungsform;
• Fig. 13, 14 und 15 zeigen den Fig. 5, 6 und 7 entsprechende Ansichten einer dritten Ausführungsform;
• Fig. 16, 17, 18 und 19 zeigen den Fig. 1 bis 4 entsprechende Ansichten von Ausführungsbeispielen mit dem universell einsetzbaren Dichtungsglied.

The variety of pressure exertion can be increased even more if additional zones of increased pressure are applied, which can be achieved, for example, by the provision of pressure members, for example according to DE-A 2 230 139. Exemplary embodiments of the invention are shown in the drawing.

• Fig. 1 shows schematically the view of a pair of rollers, of which the upper roller is designed as a roller according to the invention with zones of reduced pressure compared to the space between crosshead and hollow roller, partly in section;
• Fig. 2 shows a cross section along the line II-11 in Figure 1 on a slightly enlarged scale.
• FIG. 3 shows a view corresponding to FIG. 1 of a pair of rollers, in which the top roller is equipped with stamps which can work both as vacuum elements and as overpressure elements;
• Fig. 4 shows a section along the line IV-IV in Fig. 3;
• 5 shows an enlarged partial cross section through a roller according to the invention with a first embodiment of a stamp;
• FIG. 6 shows a cross section corresponding to FIG. 5 on a reduced scale, in which the hydraulic circuit diagram of the roller according to FIG. 5 is given;
• Fig. 7 shows a view of the stamp of Fig. 5 from above;
• Fig. 8 shows schematically a calender stack in which the roller according to the invention is indicated by hatching;
• Fig. 9 shows a partial longitudinal section through the end of a roller according to the invention with an inner stroke;
• Figures 10, 11 and 12 show views of another embodiment corresponding to Figures 5, 6 and 7;
• Figures 13, 14 and 15 show views corresponding to Figures 5, 6 and 7 of a third embodiment;
• 16, 17, 18 and 19 show FIGS. 1 to 4 corresponding views of exemplary embodiments with the universal sealing member.

The roller arrangement shown in FIGS. 1 and 2 comprises a lower roller 10 and an upper roller 100, between which a web 30 is subjected to a pressure treatment in the nip 31. The lower roll 10 is a conventional solid roll. The upper roller 100, on the other hand, comprises a rotating hollow roller 1, the outer circumference 2 of which forms the working roller circumference and which is traversed in length by a stationary crosshead 3, which leaves distance on all sides to the inner circumference 4 of the hollow roller 1, so that it bends within the hollow roller 1 can, without coming into contact with the inner circumference 4.

The pins 21 of the lower roller 10 and the ends 5 of the crosshead 3 protruding from the hollow roller 1 at the ends are guided in the roller stand and are pressed against one another by suitable loading devices, not shown.

The hollow roller 1 can be rotatably supported at its ends on the crosshead 3 by bearings not shown in FIGS. 1 and 2. In an alternative embodiment, the hollow roller 1 is on the crosshead 3 in the working plane W i.e. 1 parallel to the plane of the drawing of the axes of the two rollers 10 and 100, and can move as a whole relative to the crosshead 3 in this plane.

The space 6 between the crosshead 3 and the inner circumference 4 of the hollow roller 1 is sealed at the ends by end cross seals, not shown, and can be filled with pressure fluid via a feed line 7, which can be returned to the reservoir 9 via a line 8. A pressure relief valve 11 is arranged in the line 8, which allows a predetermined pressure to be maintained in the intermediate space 6. The supply line 7 opens into the intermediate space 6 at the left end in FIG. 1, the return line 8 at the right end. In this way, there is a flow in the longitudinal direction of the intermediate space, which leads to an equalization of the temperature of the hollow roller 1 when the pressure fluid also serves to influence the temperature. The hydraulic fluid is removed from the reservoir and brought to pressure by a pump 12 to which the supply line 7 is connected.

This pressure prevails in the hollow cylindrical intermediate space 6, which has no subdivisions, everywhere in the same way, so that it is without Additional measures would not exert any force effects on the hollow roller 1, which would result in the same being displaced or exerted on the effective plane W. The hollow roller 1 is only "inflated" by the pressure in the intermediate space 6, without showing any other effects which are recognizable from the outside.

Now, however, zones 13 are formed in the hollow roll 1 on the side remote from the roll gap 31, in which the pressure prevailing in the intermediate space 6 is left out. The length of the zones is indicated by the small brackets. In the embodiment of Figures 1 and 2 there are six such zones, but this number is by no means mandatory.

The zones 13 are formed by annular sealing elements 14, which are guided in cylindrical blind bores 15 on the upper side of the crosshead 3 and bear with an appropriately designed end face sealingly against the inner circumference 4 of the hollow roller 1. Each of the blind bores 15 is connected via a connecting line to one of a plurality of supply lines 16 (FIG. 2) and via this to a control device 17, by means of which a pressure can be maintained inside the annular sealing members 14, that is to say in the zones 13, which is lower than the pressure in the intermediate space 6 and which can be controlled independently in the individual punches 14 or in groups of punches 14 depending on the number of feed lines 16. In the simplest case, the control device 17 simply connects the zones 13 to the storage container 9, so that the zones 13 are practically depressurized.

In this way, "holes" or "vacancies" in which the pressure does not prevail are, as it were, left out in the otherwise uniform pressure in the intermediate space 6. As a result, the application of pressure to the liquid in the intermediate space 6 is made uneven. The zones 13 lie with respect to the meridian plane of the roller 100, i.e. 1 opposite the longitudinal median plane of the roller 100 or the crosshead 3 perpendicular to the plane of the drawing in FIG. 1, which are again indicated in FIG. 1 by small brackets and in which the full pressure prevails in the intermediate space 6. Since there is no or only a reduced pressure in these zones 18 above the meridian plane in the zones 13, the overall effect of the presence of the zones 13 is essentially the same as if local on the underside of the crosshead 3, that is to say in those given by the zones 18 Areas exerted a pressure corresponding to the pressure in the intermediate space 6 which, according to FIG. 1, the hollow roller 1 with respect to the crosshead 3 downwards, ie towards the roll gap 31, to move. Thus, although in the roller 100 the annular sealing members 14 are arranged on the top of the crosshead 3, the force is exerted downwards. This is achieved by the basic principle of filling the space 6 all around, that is to say without longitudinal subdivisions, with hydraulic fluid under a uniform pressure.

In Fig. 1 two further plungers 19 are shown, which are arranged on the underside of the crosshead 3 and can exert a positive force against the underside of the inner circumference 4 of the hollow roller 1. They are supplied with hydraulic fluid by a pump 20. Of course, the pressure for supplying the pressure stamp 19 can also be derived from the pump 12. Since the pressure stamps 19 are merely additional elements by means of which the line pressure distribution caused by the zones 13 can be optionally modified, the pressure stamps 19 with their supply lines and their pump 20 are shown in dash-dot lines.

3 and 4, an essential further development of the idea of the invention is shown. As far as the parts correspond to those of FIG. 1, the reference numbers are the same.

3 and 4, a lower roller 200 is provided which, like the upper roller 100 according to FIGS. 1 and 2, comprises a hollow roller 1 which rotates around a crosshead 3 'and works against an upper roller 10 and exerts pressure on one Goods web 30 exercises. In the case of the roller 200 as well, the space 6 between the inner circumference 4 of the hollow roller 1 and the crosshead 3 'can be completely filled with pressure fluid under a selectable pressure via a feed line 7 and a return line 8, but in this case the pressure distribution which is uniform per se is interrupting and a line pressure generating stamp 24 is arranged on the side of the roll gap 31. The punches 24 of the roller 200 differ from the ring-shaped sealing members 14 of FIGS. 1 and 2 in that it is possible with them both via the feed lines 26 in the zones 23 separated by the punches to reduce the pressure relative to the intermediate space 6 and also to set a higher pressure than the gap 6. By means of the control device 27, the interior of the punches 24 can thus be selectively via the line 25, e.g. be connected to the reservoir 9, so that there is practically no pressure in them, or a pressure higher than the pressure in the intermediate space 6 can be applied to the punches 24 in the zones 23 by means of the pump 22.

In this way, the punches 24 have two functions: if a lower pressure prevails in the zones 23 than in the intermediate space 6, then the pressure in the intermediate space 6 has the upper hand in the zones opposite to the zones 23, which are not marked in FIG. 3, and arises a force that the hollow roller 1 tends to pull away from the counter roller 10. Thus, if the hollow roller 1 is not supported at the ends, but rather can be displaced as a whole in relation to the crosshead 3 'in the working plane W, the hollow roller 1 can be released from the roll gap 31 in this way, for example in order to be able to thread the web 30. In this case, the stamps 24 thus act as "vacuum elements". If, however, an increased pressure is generated in the punches 24 compared to the intermediate space 6, they act as upwards according to FIG. H. force-exerting elements directed against the roll gap 31, by means of which a line pressure in a certain distribution can be achieved. In this case, the stamps 24 are “overprint elements”.

Practical embodiments of the stamp 24 shown only schematically in FIGS. 3 and 4, which can work both as negative pressure elements and as positive pressure elements, are explained in FIGS. 5 to 15. The roller 2oo is chosen as an application example, but everything that has been said also applies analogously to the roller 100.

5 to 7, the simplest stamp 24 is shown. The stamp 24 consists of a pot-shaped casting 32 made of a suitable bronze, which is inserted with its open side down into the blind bore 15 and is movable therein in the manner of a piston, the seal being provided by a circumferential sealing ring arranged at the lower edge of the pot-shaped casting 32 33 takes place. At the bottom 34 of the pot-shaped casting 32, a support surface 34 is formed in its shape which is adapted to the inner circumference 4 of the hollow roller 1 and by means of which the stamp 24 rests against the inner circumference 4 of the hollow roller 1. The system is shown in FIGS. 5, 6; 10, 11 and 13, 14 from below against the top of the hollow roller 1, ie in the same direction as in the embodiment of FIGS. 3 and 4.

The support surface 34 comprises a closed peripheral web 35 protruding in a web-like manner against the inner circumference 4 of the hollow roller 1 and a connecting web 36 located in the active plane. The edge 35 and the connecting web 36 delimit two hydrostatic pressure chambers 37, 38 adjacent to one another in the circumferential direction of the hollow roller 1 the support surface 34 form a shallow depression. In a practical exemplary embodiment, the edge 35 has an outer diameter of approximately 180 to 200 mm and the hydrostatic pressure chambers are 6 to 8 mm deep.

The cylinder space 40 formed inside the blind bore 15 below the plunger 24 is connected to the hydrostatic pressure chambers 37 and 38 via two throttle bores 39. In addition, channels 41 and 42 leading from the hydrostatic pressure chambers 37 and 38 into the cylinder space are provided in the "bottom" of the pot-shaped casting 32 forming the punch 24, in which in the exemplary embodiment ball check valves designed check valves 43 are arranged, which are arranged in the Open in the direction towards the cylinder space 40, lock in the opposite direction.

As can be seen from FIG. 5, three feed lines 26 are provided in the crosshead 3 ′, of which the one on the right in FIG. 5 is connected to the cylinder space 40. Another feed line 16 is connected to an adjacent stamp 24, etc. In many cases it is sufficient if a line pressure which is variable over the width of the web but symmetrical to the center of the web can be exerted. In such a case, the three feed lines 26 can supply six punches 24, as are provided in the exemplary embodiment in FIG. 3. It goes without saying that other numbers of stamps can also be present. If the number of stamps is even and only a line pressure distribution that is symmetrical to the center is important, half the number of stamps is sufficient as the number of the supply line. For higher demands on the independent controllability, a separate supply line must be provided for each stamp 24.

The punch 24 is continuously, i.e., supported by a helical compression spring 44, which is supported against the bottom of the blind bore 15 and against the bottom of the pot-shaped casting 32. even without liquid pressure, held in contact with the inner circumference of the hollow roller 1. When liquid pressure is presented in the intermediate space 6, an application pressure also acts in the overhang 27, i.e. the projection on the underside of the head of the stamp 24. This overhang 27 results for structural reasons when the pressure chambers 37, 38 must be given at least the same cross section as the blind bore 15.

If the plunger 24 is to function as an overpressure element, hydraulic fluid is brought in via the respective supply line 26 at a pressure which is higher than the pressure in the intermediate space 6. The cylinder space 40 fills with this hydraulic fluid and hydraulic fluid passes through the throttle bores 39 into the hydrostatic pressure chambers 37, 38 until they are filled. The cross section of the hydrostatic pressure chambers 37 and 38 is slightly larger than the cross section of the pressure in the cylinder chamber 40, i.e. in cross section of the blind bore 15. As a result, the hydraulic fluid in the hydrostatic pressure chambers 37, 38 is able to push the plunger 24 a little from the inner circumference 4 of the hollow roller 1. Hydraulic fluid then flows over the edge F5 into the intermediate space 6. Due to this loss of fluid, the pressure in the hydrostatic pressure chambers 37, 38 drops almost instantaneously due to the presence of the throttle bores 39, as a result of which the gap formed at the edge 35 closes again and the pressure in the hydrostatic pressure chambers 37, 38 rises again. In this way, an equilibrium is formed, the edge 35 and the connecting web 36 always running on a thin liquid layer and not coming into metallic contact with the inner circumference 4 of the hollow roller 1.

Two hydrostatic pressure chambers 37, 38 are provided so that the stamp 24 on the inner circumference 4 of the hollow roller 1 can be better stabilized and the supporting liquid layer is formed more uniformly.

In this way, a force can be exerted against the inner circumference 4 of the hollow roller 1 that is higher than the force that would result if the pressure in the intermediate cross-section 6 had an effect in the cross section of the hydrostatic pressure chambers 37, 38.

In the other operating mode, in which the stamp 24 works as a vacuum element, the responsible feed line 26 is connected directly to the storage container, for example. The cylinder space 40 is thereby practically depressurized. The punch 24 is nevertheless held by the spring 44 in contact with the inner circumference 4 of the hollow roller 1, even if there is still no pressure in the space 6. However, if such a pressure is built up there, the circulation of the hollow roller 1 and the adhesion of the pressure fluid on the inner circumference 4 pressure fluid is introduced into the hydrostatic pressure chambers 37, 38 from the space 6 over the edge 35, which would normally lead to the filling of these pressure chambers and the build-up of a hydrostatic pressure therein after some time. In order to counteract this pressure build-up, the check valves 43 are provided which open at a low pressure in the pressure chambers 37, 38 and allow the pressure fluid to flow into the cylinder space 40. In this way, a "negative pressure" prevails in zone 23 and in cylinder space 40, that is, a pressure below the pressure in intermediate space 6.

The presence of the check valves 43 is decisive for the double function of the plunger 24. These block the liquid passage when functioning as a hydrostatic overpressure element, but do not provide any appreciable resistance to the liquid outflow when functioning as a vacuum element.

6 shows a hydraulic circuit diagram of the roller. The pump 12 generates pressure fluid with a pressure of 60 to 80 bar, which, among other things, via a line 45. reaches the reducing valve 46, in which the pressure is reduced to the desired value in the space 6 of about 30 bar. The pressure fluid is fed into the space 6 and removed from it via the line 8, passed through a heat exchanger 47, where the pressure fluid is heated or cooled as required, and fed back to the space 6 via a circulating pump 48 and the line 7. The circulation pump 48 does not need to generate large pressure differences, but only has to ensure the flow through the intermediate space 6.

Via line 49, the pressure fluid delivered by the pressure pump 12 reaches the feed line 26 and the cylinder space 40 via a three-way pressure regulator 50 and passes through the throttle bores 39 of the plunger 24 in the manner already described. The arrow 51 symbolizes the feed lines to the others Cylinder rooms 40, each of which is assigned its own pressure regulator 50, so that the pressure can be regulated individually.

3, the roller 200 is shown in an arrangement with only one counter roller 10. FIG. 8 schematically illustrates the possibility of using the roller 200 in a calender with four rollers. Due to the constant variability of the pressure from an area in which the roller 200 presses up to an area in which it acts downwards, the distribution or the sequence of the line pressures in the stacked nips A, B and C are affected.

As already mentioned, it is easily possible to design the roller 200 as such with an "inner stroke" if the hollow roller 1 is not supported on the crosshead 3 'at the ends, but in the active plane as a whole opposite to the crosshead 3' parallel to itself itself is slidably guided.

9, the hollow roller 1 can be seen, which according to the drawing can be displaced upwards or downwards relative to the crosshead 3 '. The guidance of the hollow roller 1 perpendicular to the working plane, i.e. in the direction of the web, takes place via a guide ring 52 which surrounds the end region 53 of the crosshead 3 'at a radial distance and has a fork-like guide piece 54 at the right end according to FIG. 9, the leg of which has a radial guide web 55 which is attached to a shoulder 56 of the crosshead 3 'is attached, reach around on both sides. The guide ring 52 can therefore shift from the position shown in solid lines, for example, to the position 52 'shown in dash-dot lines. According to FIG. 9, a displacement is not possible perpendicular to the plane of the drawing. The hollow roller 1 is supported on the guide ring 52 via a bearing 57, which, however, has only management tasks and is not intended to transmit forces in the active plane. In the space 6 between the hollow roller 1 and the crosshead 3 ', the punches 24 are attached on the right as shown in FIG. 9. The sealing of the space 6 to the outside, i.e. 9 to the left takes place through the mechanical seal 58.

The hollow roller 1 can thus be pulled down and pressed upwards when the crosshead 3 'is stationary, the essential thing being that, due to the double function of the punch 24, despite the double direction of force, these need only be attached to one side of the crosshead and the crosshead weakened through the blind holes 15 only on one side.

The stamp 24 'of FIGS. 10 to 12 differs first of all from the stamp 24 in that the throttle bores 39 do not open into the cylinder space 40, but into an inner chamber 60 of the stamp 24', which is a cylindrical bore of a central one from Bottom into the interior of the "pot" protruding projection 59 is formed, in which the piston-like upper end part 61 of a sleeve 63 can be moved longitudinally in a sealed manner, the lower end of which is provided in a distributor plate 65 provided with radial channels 64 on the bottom of the blind bore 15 and provided with radial channels 64 is screwed in, by means of which a connection of the sleeve 63 located in the axis of the blind bore 15 is also possible with feed lines 66 located radially further outward.

Due to the arrangement shown, pressure which is different from the pressure in the cylinder chamber 40 can be supplied to the inner chamber 60 from any of the supply lines 66. Parts 61, 63 and 64 form a line arrangement which works in any position of the plunger 24 'in the blind bore 15.

The purpose of this design is that the hydrostatic pressure chambers 37, 38 can be supplied with a pressure which is no longer coupled to the pressure in the cylinder chamber 40. It is therefore also no longer necessary for the effective area of the cylinder chambers 37, 38 to be larger than that of the part of the plunger 24 'which is displaceable in the blind bore 15. Via the feed lines 66, a volume-controlled pressure fluid quantity is fed to the hydrostatic chambers 37, 38 separately from the feed lines 26. That per unit of time constant, forcibly supplied hydraulic fluid volume flows off over the edge 35 and ensures the supporting fluid layer between the contact surface 34 and the inner circumference 4 of the hollow roller 1. The pressure in the hydrostatic chambers 37, 38 adjusts itself automatically and has no relation to the pressure in the cylinder chamber 40.

Another important difference from the stamp 24 is that in the stamp 24 'outside the edge 35 of the hydrostatic pressure chambers 37, 38 there is provided a peripheral discharge chamber 70 which communicates with the cylinder chamber 40 via a channel 67 and a check valve 43 is connectable. As can be seen from FIG. 12, the two discharge chambers 70 are semicircular and provided outside the edge 35. The purpose of the lead. _"'The chambers 70 is ut at the edge. _35:-etende trap hydraulic fluid and to feed the cylinder chamber 40 when the plunger 24' operates as a negative pressure producing member, that is, when the pressure in the space 6 is larger than that in the hydrostatic chambers 37 38. Then quite a lot of pressure fluid is carried along the inner circumference 4 of the hollow roller 1 and is introduced into the hydrostatic pressure chambers 37, 38 without the discharge chambers 70. This largely prevents the discharge chamber 70, which is on the side of the plunger opposite to the direction of rotation of the hollow roller 1 Due to the installation direction of the check valve 43, pressure fluid trapped at the discharge chamber 70 can flow out when operating as a vacuum element without any appreciable resistance, while, conversely, when the plunger 24 'is operated as a pressure element, the discharge chambers 70 are closed and remain ineffective The case is the cylinder chamber 40 and the respective Z Line 26 is relieved, while a pressure is maintained via the line 66, the inner chamber 60 and the throttle bores 39 in the pressure chambers 37, 38, which is just sufficient to overcome the force of the spring 44, so that the maintenance of the liquid film between the edge 35 and the inner circumference 4 of the hollow roller 1 is guaranteed. However, this pressure is much lower than the pressure in the space, so that the function as a vacuum element is not affected.

The circuit diagram according to FIG. 11 differs from the circuit diagram according to FIG. 6 only in the separate supply of the pressure fluid via the line arrangement 66, 63. This is supplemented by a current regulator 7zvalve 68 leading to the supply lines 66, which, as already mentioned, the Quantity of the hydraulic fluid supplied to the hydrostatic pressure chambers 37, 38 is determined. Each punch 24 'or each group of such stamps located symmetrically is assigned its own flow control valve 68, in order to ensure that each punch 24' or each group of such stamps, independently of the others, receives exactly the amount of pressure fluid which is allocated to them, the pressures adjust by yourself.

In the embodiment 24 "according to FIGS. 13 to 15 there is no separate supply of the pressure fluid to the hydrostatic pressure chambers 37 and 38, but instead the pressure prevailing therein, as with the plunger 24, is a function of the pressure prevailing in the cylinder space 40 Accordingly, in addition to the feed lines 26, there are no further feed lines (such as 66 in FIGS. 10-12). Drainage chambers 80 are also provided for the stamp 24 ″, which via non-return valves 43 that open towards the cylinder space 40, are connected to this. The check valve 43 is located in channels 67. The discharge channels 80 are also approximately semicircular in shape and upstream of the hydrostatic pressure chambers 37, 38 in the circumferential direction. In contrast to the punch 24 ', however, the ends of the semicircular discharge channels 80 in the punch 24 "are connected to one another by channel parts 80', so that the discharge channel 80 as a whole forms a discharge zone surrounding the respective hydrostatic pressure chamber 37 or 38. The hydrostatic pressure chambers 37, 38 are separated all around against the discharge channel 80 by an edge 35 'forming an annular sealing web. The hydrostatic pressure chambers 37, 38 thus form, as it were, islands within the discharge channel 80.

The stamp 24 "is again formed by a pot-shaped casting 72, which is arranged with the open side downward in the blind bore 15. However, an inner chamber 90 is divided into the stamp 24" by an intermediate floor 73 arranged halfway up, from which the throttle bores 39 opening into the hydrostatic pressure chambers 37, 38 start. A check valve 74 opening into the inner chamber 90 is arranged in the intermediate floor 73. In addition, in the side wall of the pot-shaped casting 72 in the region of the inner chamber 90, a check valve 75, which communicates with the space 6 and opens into the inner chamber 90, is arranged.

The special feature of the stamp 24 "is that the discharge chambers 80 can be used as hydrostatic pressure chambers in the event of operation as an overpressure element. For this it is essential that the channels 67 containing the check valves 43 are provided with throttle bores 76 which channel 67 in the Connect the area between the check valves 43 and the inner circumference 4 of the hollow roller 1 to the cylinder space 40.

When operated as an overpressure element, pressure fluid is supplied to the cylinder space 40 at a pressure which is higher than the pressure in the cylinder space 6. The pressure fluid passes through the check valve 74 into the inner chamber 90 and from there via the throttle bores 39 into the hydrostatic chambers 37, 38. The check valve 75 closes here, so that the pressure in the inner chamber 90 cannot collapse.

In addition, the pressure fluid from the cylinder chamber 40 enters the discharge chambers 80 via the throttle bores 76 and the channels 67, that is to say in in this case also act as a hydrostatic chamber.

The total area of the hydrostatic chambers 37, 38 and the discharge chambers 80 must be larger than the effective area of the plunger 24 "in the blind bore 15, so that the plunger 24" is properly supported on a liquid film formed between the latter and the inner circumference 4. The support surface of the punch 24 bearing against the inner circumference 4 must therefore necessarily be larger than the cross section of the hole 15, i.e. there is an overhang 78 on the underside 77 of the head part of the stamp 24 forming the supporting surface, as in FIG. an annular, radially over the circumference of the lower part of the punch 24 "protruding active surface, which acts on the pressure fluid located in the space 6 and exerts a force pushing the punch 24" against the inner circumference 4 of the hollow roller 1.

This circumstance has a special meaning if the plunger 24 "is operated as a vacuum element, ie if the pressure in the intermediate space 6 is greater than the pressure in the cylinder space 40 or in the cylinder space 40 there is no pressure at all of the hollow roller 1 during the circulation into the discharge chambers 80 from the intermediate space 6 discharged hydraulic fluid via the check valves 43 into the cylinder space 40. However, the high pressure in the intermediate space 6 acts in the overhang 78 and presses the stamp 24 "with a considerable force against the Inner circumference 4 of the hollow roller 1, which can lead to malfunctions, since in this case a liquid film is not normally maintained between the support surface of the punch 24 "and the inner circumference 4 as in overpressure operation. In order to avoid this pressure, which can lead to metallic friction, To defuse and at the same time to create a certain liquid film again is the back stop valve 75 provided. This valve namely pressurized fluid from the space 6 into the inner chamber 90 and is prevented by the check valve 74 from flowing into the cylinder space 40. However, it flows through the throttle bores 39 into the hydrostatic pressure chambers 37, 38, which in this case also maintain their function as a hydrostatic pressure chamber even in negative pressure operation and generate a force which is opposite to the force acting on the overhang 78. The plunger 24 "is relieved hydraulically in this way, the surfaces of the overhang 78 and the hydraulic pressure chambers 37 and 38 being coordinated with one another. In addition, the passage of liquid from the hydrostatic pressure chambers 37 and 38 at least partially produces a liquid film which has a prevents metallic contact.

FIGS. 16 to 19 once again explain the use of pressure members which can exert pressure which is both elevated and reduced in relation to the environment.

The roller arrangement shown in FIGS. 16 and 17 comprises an upper roller 10 and a lower roller 100, between which a web 30 is subjected to a pressure treatment in the nip 31. The top roller 10 is a conventional solid roller. The lower roll 100, on the other hand, comprises a rotating hollow roll 1, the outer circumference 2 of which forms the working roll circumference and which is traversed in length by a stationary crosshead 3, which on all sides leaves distance from the inner circumference 4 of the hollow roll 1, so that it bends within the hollow roll 1 can, without coming into contact with the inner circumference 4.

The pins 21 of the top roller 10 and the ends 5 of the crosshead 3 protruding from the hollow roller 1 at the ends are guided in the roller stand and are optionally pressed against one another by loading devices (not shown).

The hollow roller 1 can be rotatably supported at its ends on the crosshead 3 by bearings not shown in FIGS. 16 and 17. In an alternative embodiment, the hollow roller 1 is on the crosshead 3 in the working plane W, i.e. in the connection plane of the axes of the two rollers 10 and 100, which is parallel to the plane of the drawing in FIG. 16, and as a whole can shift relative to the crosshead 3 in this plane.

In the space 6 between the crosshead 3 and the inner circumference 4 of the hollow roller 1, a longitudinal chamber 14, which is located on the side of the roll gap 31, is divided by longitudinal seals 13 running along the crosshead 3 and diametrically opposite one another at the widest point of the cross section, which ends is sealed by end cross seals, not shown, and can be filled with pressure fluid via a feed line 7, which can be returned to the reservoir 9 via a line 8. In line 8, a pressure relief valve 11 is arranged, which allows a predetermined pressure to be maintained in the longitudinal chamber 14. The supply line 7 opens into the longitudinal chamber 14 at the left end in FIG. 16, the return line 8 at the right end. In this way, there is a flow in the longitudinal direction of the longitudinal chamber 14, which leads to an equalization of the temperature of the hollow roller 1 when the pressure fluid also serves to influence the temperature. The hydraulic fluid is removed from the reservoir and brought to pressure by a pump 12 to which the supply line 7 is connected.

Zones 23 are formed in the longitudinal chamber 14 of the hollow roller 1, in which the pressure prevailing in the longitudinal chamber 14 is left out. The length of the zones is indicated by the small brackets. In the embodiment of FIGS. 16 and 17 there are six such zones, but this number is by no means mandatory.

The zones 23 are formed by sealing members in the form of stamps 24, which are guided in cylindrical blind bores 15 on the upper side of the crosshead 3 and bear sealingly against the inner circumference 4 of the hollow roller 1 with an appropriately designed end face. Each of the blind bores 15 is connected via a connecting line to one of a plurality of supply lines 26 (FIG. 17) and via this to a control device 17 by means of which a pressure can be maintained in the area of the punch 24, that is to say in the zones 23, which deviates from the pressure of the longitudinal chamber 14 and which in the individual punches 24 or in groups of punches 24 depending on the number of supply lines 26 can be controlled independently.

It is essential that the punches 24 are designed such that the pressure in them can be both higher and lower than the pressure in the longitudinal chamber 14. In the simplest case of the latter alternative, the control device 17 simply connects the punches 24 to the reservoir 9 , so that the stamp 24 are practically depressurized.

The inherently uniform pressure in the longitudinal chamber 14 is therefore modified in the zones 23 by exerting additional individual forces there at higher pressures in the punches 24 or by "holes" from the uniform pressure cushion in the longitudinal chamber 14 at lower pressures in the punches 24 be spared. Both can be used to influence the line pressure distribution in the roll gap 31 in different ways.

16 shows two further pressure stamps 19, which are arranged on the underside of the crosshead 3 and can exert a positive force against the underside of the inner circumference 4 of the hollow roller 1. They are supplied with hydraulic fluid by a pump 20. Of course, the pressure for supplying the pressure stamp 19 can also be derived from the pump 12. Since the pressure stamps 19 are merely additional elements by means of which the line pressure distribution caused by the zones 13 can be optionally modified, the pressure stamps 19 with their supply lines and their pump 20 are shown in dash-dot lines.

Another important application example is shown in FIGS. As far as the parts correspond to those of Fig. 16, the reference numerals are the same.

In the roller arrangement of FIGS. 18 and 19, a lower roller 200 is provided which, like the lower roller 100 according to FIGS. 16 and 17, comprises a hollow roller 1 rotating around a crosshead 3 ', which works against an upper roller 10 and exerts pressure on one Goods web 30 exercises. In contrast to the exemplary embodiment according to FIGS. 16 and 17, there is no longitudinal seal in the intermediate space 6, which seals off a one-sided longitudinal chamber. Rather, in the roller 200, the entire space 6 between the inner circumference 4 of the hollow roller 1 and the crosshead 3 'can be completely filled with pressure fluid under a selectable pressure via the feed line 7 and a return line 8.

This pressure prevails in the hollow cylindrical intermediate space 6, which has no subdivisions, in the same way everywhere, so that it would not exert any force effects on the hollow roller 1 without additional measures, which leads to a displacement or exertion of force thereof in the effective plane W. The hollow roller 1 is only "inflated" by the pressure in the intermediate space 6, without showing any other effects which are recognizable from the outside.

Arranged on the side of the roll gap 31, however, are the punches 24 which in themselves interrupt uniform pressure distribution and produce line pressure. By means of the punches 24 of the roller 200, it is possible both to set a lower pressure in the corresponding zones 23 divided by the punches with respect to the space 6 and also to increase the pressure with respect to the space 6. By means of the control device 27, the interior of the punches 24 can thus be selectively via the line 25, e.g. be connected to the reservoir 9, so that there is practically no pressure in them, or a pressure higher than the pressure in the intermediate space 6 can be applied to the punches 24 in the zones 23 by means of the pump 22.

If the pressure in the zones 23 is lower and the space 6 is completely filled with hydraulic fluid, "holes" or "vacancies" in which the pressure does not prevail are, as it were, cut out in the otherwise uniform pressure in the space 6. As a result, the application of pressure to the liquid in the intermediate space 6 is made uneven. The zones 23 lie with respect to the meridian plane of the roller 200, i.e. opposite to the horizontal longitudinal center plane of the roller 200 or the crosshead 3 perpendicular to the plane of the drawing, which are again indicated by small brackets in FIG. 18 and in which the full pressure in the space 6 prevails. Since there is no or only a reduced pressure in these zones 18 above the meridian plane in the zones 23, the overall effect of the presence of the zones 23 is essentially the same as if locally on the underside of the crosshead 3, that is to say in those given by the zones 18 Areas exerted a pressure corresponding to the pressure in the intermediate space 6 which, according to FIG. 18, the hollow roller 1 with respect to the crosshead 3 downwards, ie away from the roll gap 31, the aim is to shift. In this case, although the punches 24 are arranged on the top of the crosshead 3, the force is exerted downwards. This results from the fact that the space 6 is filled with hydraulic fluid under a uniform pressure all around, that is to say without longitudinal divisions.

In this way, the punches 24 have two functions: if a lower pressure prevails in the zones 23 than in the intermediate space 6, then the pressure in the intermediate space 6 in the zones 23 opposite, designated 18 in FIG. 18, has the upper hand and arises a force that the hollow roller 1 tends to pull away from the counter roller 10. Thus, if the hollow roller 1 is not supported at the ends, but rather can be displaced as a whole with respect to the crosshead 3 'in the working plane, the hollow roller 1 can be lifted off the roll gap 31, for example in order to be able to thread the web 30. In this case, the stamps 24 thus act as "vacuum elements". However, if a higher pressure than the space 6 is generated in the stamps 24, they act as upwards according to FIG. force exerting elements directed against the roll gap 31, by means of which a line pressure in a certain distribution can be achieved. In this case, the stamps 24 are "overprint elements".

Practical embodiments of the stamps 24, which are only shown schematically in FIGS. 16 to 19 and which work both as vacuum elements and as overpressure elements and can be used both in the roller 100 and in the roller 200, are already based on FIGS. 5 to 15 have been explained. A roller corresponding to roller 200 was selected as an application example. If the pressure in the intermediate space 6 was mentioned, then in the event that the punch 24 is arranged in a roller with longitudinal seals 13 corresponding to the roller 100, the longitudinal chamber 14 is to be understood accordingly.

Claims (11)

1. A roll with controllable line pressure, comprising a rotating hollow roll (1) constituting the working roll periphery and a stationary crosshead (3) extending longitudinally through the roll and leaving an annular space between it and the inner periphery (4) of the hollow roll (1), transverse end seals by means of which the gap (6) extending around the crosshead (3) between the hollow roll (1) and the crosshead (3) is axially sealable between the hollow roll (1) and the crosshead (3), a device for supplying pressure fluid at a controllable pressure to at least a part of the gap (6) bounded in the peripheral direction, and zones (13, 23) divided off from the part of the gap (6) by annular sealing elements (14, 24) disposed in the part of the gap (6) and abutting the inner periphery (4) of the hollow roll (1), feed ducts (16, 26) disposed in the crosshead (3) opening into the zones and a valve arrangement being inserted therein for connecting the zones (13, 23) to a region at a lower pressure than the part of the gap (6), characterised in that the entire gap (6) outside the zones (13, 23) can be supplied with pressure fluid at a uniform pressure everywhere.

2. A roll according to claim 1, characterised in that the zones (23) can also be optionally connected to a region at a higher pressure than the gap (6).

3. A roll according to claim 2, characterised in that the sealing elements dividing off the zones (23) are in the form of piston-like elements (24, 24', 24") movable in cylinder pocket bores (15) in the crosshead (3') and at right angles to the axis thereof, feed ducts (26) are provided in the crosshead (3_') in connection with the cylinder space (40) on the side of the base of the cylinder pocket bores (15), at least one hydrostatic pressure chamber (37, 38, 70, 81) having a peripheral edge and open towards the inner periphery (4) of the hollow roll (1) is formed on the supporting area on the end face of the pistons (24, 24', 24") adjacent the inner periphery (4) of the hollow roll (1), choke bores (39) opening into the hydrostatic pressure chamber (37, 38) are provided in the piston (24, 24', 24") and are adapted to fill the hydrostatic pressure chamber (37, 38) with pressure fluid, and at least one channel (41, 47) connecting the hydrostatic pressure chamber (37, 38, 70, 80) to the cylinder space (40) is provided in the piston (24, 24', 24") and a non-return valve (43) opening towards the cylinder space (40) is disposed in the channel.

4. A roll according to claim 3, characterised in that the choke bores (39) are connected to the cylinder space (40).

5. A roll according to claim 3, characterised in that the piston (24') has an inner chamber (60) which is connected by the choke bores (39) to the hydrostatic chamber (37, 38) and, via a line arrangement (61, 63) for moving the piston (24') In the cylinder pocket bore (15), is connected to a feed duct (66) in the crosshead (3_') separate from the feed duct (26) to the cylinder space (40).

6. A roll according to any of claims 2 to 5, characterised in that a drain chamber (70, 80) disposed in front of the hydrostatic pressure chamber (37, 38) at the outer edge (35) in the peripheral direction is provided in the supporting area and is connected to the cylinder space (40) via a non-return valve (43) which opens towards the cylinder space (40).

7. A roll according to any of claims 2 to 6, characterised in that the piston (24") has an inner chamber (90) connected by the choke bores (39) to the hydrostatic pressure chamber (37, 38), connected to the cylinder space (40) by a non-return valve (74) opening towards the inner chamber (90), and connected to the gap (6) between the crosshead (3') and the hollow roll (1) by a non-return valve (75) opening towards the inner chamber (90), but otherwise closed, the piston (24") projects radially over the cross-section of the cylinder pocket bore (15) towards the axis thereof and forms an overhang (78) via which the piston (24") can be pressed against the inner periphery (4) of the hollow roll (1) by the pressure prevailing in the gap (6) between the crosshead (3_') and the hollow roll (1), and the hydrostatic effective surface area of the overhang (78) is adapted to the hydrostatic surface area of the hydrostatic pressure chamber (37, 38) connected by the choke bores (39) to the inner chamber (90), so as hydraulically to relieve the piston (24").

8. A roll according to claim 7, characterised in that the channel (67) containing the non-return valve (43) is connected to the cylinder space (40) by a choke bore (76) outside the inner chamber (90).

9. A roll according to any of claims 2 to 8, characterised in that the drain chamber (80) surrounds the hydrostatic pressure chamber (37, 38) in a ring and the hydrostatic pressure chamber (37, 38) is separated from the drain chamber (80) by an annular web-like sealing edge (35).

10. A roll according to any of claims 1 to 9, characterised in that a number of pistons (14; 24, 24', 24") are provided on the side of the crosshead (3, 3') facing the nip (31).

11. A roll according to any of claims 1 to 10, characterised in that additional elements (19) are provided and form zones at a pressure greater than the pressure of the gap (6).

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